We propose to complete an analysis of data which measure the impact of legislation that raised the legal drinking age in Massachusetts from 18 to 20 in 1979. This project was originally approved by the NIAAA Psycho Social Research Section for three years, but because of events beyond our control, funding has stopped after 2 years. We are seeking funding for the final year to complete the analyses. Massachusetts is being compared to Upstate New York which retained a legal drinkig age of 18 years. Random digit dailing telephone surveys of 1000 16-19 year olds were completed in Massachusetts and New York prior to the legal change and twice at yearly intervals following the law. We will compare responses to teenagers in each state before and after enactment of questions about their drinking practices, psychoactive drug use, driving practices, frequency of driving after drinking, and or use of psychoactive substances, and non-fatal accident involvement. Fatal accident data reported by each state to the U.S. Department of Transportation have been compared in each state for three years preceding and 1 1/2 years following the law. We propose to extend that analysis through three years after enactment as originally proposed and to analyze non-fatal accident involvement. Preliminary assessment by other researchers of laws raising legal drinking ages across the country have thus far revealed a mixed impact from state to state on teenage non-fatal and fatal accident involvement. This project devotes greater attention than those studies to understanding police and judicial enforcement of the law. Police officers at all levels of command accross Massachusetts have been interviewed and arrest data and judicial processing have been monitored. The interviews and monitoring will continue in this third year. Our surveys of teenagers have also systematically explored their perceptions of enforcement. Only through attention to those factors over time can we begin to understand under what circumstances changes in legal drinking ages reduce teenage drinking and traffic accident casualties. Our prospective natural experiment permits us to control for the effects of many potential confounding variables, and provides a much deeper understanding than other previous or ongoing studies about the conditions under which the legislative approach can achieve or may fail to achieve its intended objectives.